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Parallel Rules

Parallel rules help draftsmen, surveyors, cartographers, architects, and navigators draw accurate parallel lines. The instrument comes in two main forms: two rectangular straight edges connected by brass or silver hinges, or a single frame surrounding a roller. The first type was known in Europe by 1600, while Englishman A. George Eckhardt is credited with inventing the second in 1771. The parallel rule was superseded for most uses by the T-square in the 19th century, but navigators continue to use parallel rules in conjunction with gridded charts.

The mathematics collections contain about twenty parallel rules and combination instruments, dating from the late 18th century to the late 20th century and ranging in length from 6 to 24 inches. The objects are made from ebony and other woods, brass, German silver, and plastic. They were manufactured in the United States, England, Italy, and Taiwan. They were used for military surveying, in navigation, in business, in art and technical drawing, and for placing handles on caskets. Several of the objects in this group illustrate innovations added to the basic instrument.

Acknowledgement

The digitization of this group of artifacts was made possible through the generous support of Edward and Diane Straker.

This 21" German silver hinged parallel rule has two small knobs for positioning the instrument. Brass round pieces cover the screws securing the two hinges. An indentation is on both blades at the center of the rule, with a line marking the center. The edges of the top blade are marked as a rectangular protractor, and the edges of the bottom blade are marked for nautical compass points.

The center of the top blade is marked: U. S. C. & G. S. NO. 331. The right end of the top blade is marked: CAPT. FIELD'S IMPD. The right end of the lower blade is marked: H. HUGHES & SON LTD. LONDON. The left end has the firm's "HUSUN" logo, with a sun above the letters and waves below the letters.

Capt. William Andrew Field (about 1796–1871) of England added a protractor and compass scales to hinged parallel rules in 1854. This made it easier for ship navigators to move the rule without losing track of the ship's course. Henry Hughes & Son made marine and aeronautical navigational instruments in London from 1828 to 1947 and incorporated in 1903. According to the accession file, the U.S. Coast & Geodetic Survey acquired this rule on August 21, 1919, and last issued it on September 5, 1922. Compare to MA*309662 and MA*309663.

This 21" German silver hinged parallel rule has two knobs for positioning the instrument. Brass round pieces cover the screws securing the two hinges. The edges of the top blade are marked as a rectangular protractor, and the edges of the bottom blade are marked for nautical compass points.

The right end of the upper blade is marked: CAPT. FIELD'S IMPD. The center of the lower blade is marked: U. S. C. & G. S. NO. H. 398. The left end has the firm's "HUSUN" logo for the London instrument maker H. Hughes & Son, with a sun above the letters and waves below the letters. A circle around the logo is marked: REGISTERED TRADE MARK (/) GT BRITAIN.

Capt. William Andrew Field (about 1796–1871) of England added a protractor and compass scales to hinged parallel rules in 1854. This made it easier for ship navigators to move the rule without losing track of the ship's course. Henry Hughes & Son made marine and aeronautical navigational instruments in London from 1828 to 1947 and incorporated in 1903. According to the accession file, the U.S. Coast & Geodetic Survey acquired this rule on November 6, 1923, and last issued it on February 16, 1924. Compare to MA*309661 and MA*309663.